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Abstract:

Apparatus, e.g. a syringe, for dispensing foam includes means for
ensuring that only foam of adequate quality is dispensed. In use, the
syringe may be filled from a pressurised canister which generates foam
e.g. for therapeutic use in treating varicose veins. An initial quantity
of foam dispensed from the canister may be of inadequate quality in which
case it should not be used: the syringe includes means to ensure that
this initial quantity of foam is diverted to a waste port or to an
internal waste chamber e.g. located in the syringe plunger. Foam
dispensed after the initial quantity of poor quality foam is stored in
the main barrel of the syringe ready for administration to a patient in
need of treatment.

Claims:

1. A syringe for dispensing foam comprising: (a) a syringe plunger having
a waste chamber communicating with an inlet in a front face of the
plunger; and (b) a syringe barrel having a nozzle and a bore to receive
the plunger.

2. A syringe as claimed in claim 1 wherein the internal waste chamber is
provided with a vent which comprises either a hydrophobic vent or a hole
in a wall of the chamber.

3. A syringe as claimed in claim 1 wherein the chamber has one or more
flexible walls.

4. A syringe as claimed in claim 3 wherein the chamber is substantially
empty of air.

5. A syringe as claimed in claimed in claim 3 wherein the chamber is
retained within a rigid walled chamber or frame comprising part of the
plunger.

6. A syringe as claimed in claim 3 wherein the said flexible wall or
walls is/are substantially inextensible.

7. A syringe as claimed in claim 1 wherein the inlet to the chamber is
adjacent the syringe nozzle when the plunger is in its fully depressed
state.

8. A syringe as claimed in claim 3 wherein the flexible chamber is
contained within a space defined by rigid walls of the plunger, and vents
are provided in the said rigid walls to allow air between the chamber
walls and the said rigid plunger walls to escape when the chamber is
filling with foam.

9. A kit for providing a syringe full of foam, the kit comprising a
syringe as claimed in claim 1 together with a source of foam.

10. A kit as claimed in claim 9 wherein the source of foam is a
pressurised canister containing liquid to be foamed and gas under
pressure.

11. A method of dispensing foam using a syringe as claimed in claim 1
comprising the steps of: (a) connecting the syringe to a source of foam;
and (b) dispensing a continuous flow of foam into the syringe from the
source; (c) whereby the flow of foam initially enters the waste chamber
such that foam fills or substantially fills the said waste chamber; and
(d) the flow of foam subsequently pushes the syringe plunger back in the
syringe barrel and starts to fill the syringe.

Description:

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.
10/581,513 filed Aug. 2, 2006 which is a 371 of PCT/GB2004/005086 filed
Dec. 3, 2004 and claims priority to British Application No. 0327957.7
filed Dec. 3, 2003, the entire contents of each of which are hereby
incorporated by reference.

APPARATUS FOR DELIVERING FOAM

[0002] The present invention relates to apparatus for delivering and to
methods for filling such apparatus, e.g. from a source of foam such as a
pressurized canister which generates foam by passing liquid and gas
through a fine mesh. The invention is suitable in particular for a
precision foam such as a sterile clinical grade therapeutic foam, e.g.
for the treatment of varicose veins.

[0003] WO 00/72821 describes apparatus and methods for generating a foam
for treatment of varicose veins. In one of the embodiments described in
that patent application, foam is generated by pressurising a sclerosant
liquid and a physiological gas in a canister and releasing the mixture
through a mesh whereby a stable foam is produced suitable for injection
into varicosed blood vessels in sclerotherapy treatment. An apparatus is
described which incorporates a three-way valve attached to the outlet of
the foam generating canister. The first portion of foam generated by the
canister tends to be of poor quality, and the valve allows this foam to
be diverted to waste. The valve may then be switched over to feed foam to
a syringe for use in treatment. The disclosure of WO 00/72821 is
incorporated herein by reference.

[0004] A number of technical problems have been identified in the course
of further development of the canister based system described in WO
00/72821. These include the following. [0005] 1. When the three-way valve
is switched from the waste position to the fill position, there is a
momentary dead time when the valve is closed to both outlet ports and
flow is completely obstructed. When the valve is fully set to the fill
position and the flow re-commences, the foam is initially of poor
quality; the canister has effectively re-started its delivery of foam.
[0006] 2. In a delivery device, such as a syringe, for administering foam
to a patient, there is normally a dead space. In the case of a syringe,
this is within the bore of the luer connector on the syringe. As foam is
directed from the valve to the syringe and pushes the plunger of the
syringe back, a large bubble tends to form adjacent the plunger, which
may become incorporated within the foam and undermine its quality. [0007]
3. It is desirable to be able to inspect the foam and to determine when
consistent, good quality foam is being generated, so as to check that
foam with the correct properties is being directed into a patient's vein.
In the apparatus described in WO 00/72821, the foam is observable in a
transparent tube communicating between the canister and valve unit (ref
35 in FIGS. 10 and 11). A difficulty with this is that the foam which is
observed is some way back from the foam being delivered. Therefore it is
possible to observe adequate quality foam in the tube and still be
delivering inadequate quality foam to the syringe. [0008] 4. The waste
foam from tube 38 is not contained. [0009] 5. The use of a relatively
long tube 35 joining the canister to the valve is wasteful, since a
quantity of foam sufficient to fill the tube will always be wasted.
[0010] 6. The system is somewhat dependant on the skill of the operator
to consistently produce a syringe full of good quality foam.

[0011] Although these problems have been discussed above in connection
with the system described in WO 00/72821, they may be applicable to other
systems for generating and dispensing foam of various sorts, where a
uniform foam product having consistent, predetermined properties is
required. The contents of WO02/41872, which also relates to this field,
is incorporated herein by reference.

[0012] A number of solutions to some or all of these problems have been
devised. Some of these are described in a simultaneously filed patent
application in the name of the applicant; these solutions relate in the
main to features of a dispensing device which connects the foam source to
a syringe, the syringe being the delivery device from which foam will
ultimately be delivered for use. A number of solutions are described in
the present application, which solutions are based more on modifications
to the design of a syringe.

[0013] According to a first aspect of the invention, a syringe for
dispensing foam comprises: [0014] (a) a syringe plunger having a front
end and a back end; [0015] (b) a syringe barrel having a nozzle and a
bore to receive the plunger; [0016] (c) wherein the plunger includes a
foam inlet at the back end and a foam outlet at the front end, which
inlet and outlet are in communication with each other; and [0017] (d) a
one way valve permitting flow of foam into the inlet.

[0018] Preferably the plunger foam outlet is located adjacent the syringe
nozzle. The plunger outlet may be provided in a projection from the seal
end which projection extends into a bore of the syringe nozzle when the
plunger is in a fully depressed state.

[0019] Also according to the first aspect of the invention, an apparatus
for dispensing foam comprises a source of foam (e.g. a pressurised
canister adapted for generating foam) and a syringe as described above.
Preferably the source of foam includes an outlet of complementary form to
the foam inlet of the plunger, and adapted to make a seal with the foam
inlet.

[0020] Also according to the first aspect of the invention, an apparatus
for dispensing foam comprises a syringe as described above together with
a waste foam container having an inlet with a connector of complementary
form to the nozzle of the syringe. The waste foam container preferably
has flexible walls (e.g. is a film or foil bag) and is substantially
empty/airless before foam is dispensed into it. If the container is a
flexible bag, the walls of the bag are preferably inextensible. The waste
container may alternatively be rigid, in which case a vent is desirable
which may take the form of a simple hole or alternatively a "hydrophobic
vent", i.e. a vent having a filter of some sort which will allow gas but
not liquid to pass.

[0021] Also according to the first aspect of the invention, an apparatus
for dispensing foam comprises a source of foam, a syringe and a waste
container as described above. The syringe, foam source and waste
container may be supplied as a kit of separated elements, or two or more
of these elements may be supplied ready assembled.

[0022] A method of dispensing foam according to the first aspect of the
invention and using the above described apparatus comprises the steps of:
[0023] (a) connecting the foam source to the plunger foam inlet (unless
the source is supplied already so connected); [0024] (b) with the plunger
fully depressed, generating a substantially continuous flow of foam from
the said source and allowing an initial quantity of foam to flow from the
plunger inlet through the plunger foam outlet and thence to exit from the
syringe nozzle; and [0025] (c) without interrupting the flow of foam from
the source, blocking the syringe nozzle and causing the plunger to move
back such that foam starts to fill the syringe barrel.

[0026] The method preferably comprises attaching a waste container to the
syringe, or alternatively providing a syringe with a waste container
fitted to it as described above. In this event, the waste container may
be filled or substantially filled with the said initial quantity of foam
in step (b) above, and may provide automatically the said syringe nozzle
blocking step when so filled or substantially filled.

[0027] The syringe for dispensing foam as described may additionally
comprise a waste container within an internal chamber defined by the
plunger (or the internal plunger chamber or a part thereof may constitute
the waste container), the container being in communication with the
plunger foam inlet and having an outlet in communication with the plunger
outlet. Preferably, the communication between the waste container outlet
and the plunger outlet is via a pressure sensitive valve. The waste
container may have the optional features described above, i.e. may have
flexible walls or rigid walls and, if the latter, desirably has a vent
which is either a hydrophobic vent or a small hole.

[0028] The invention also encompasses a syringe plunger for such a
syringe, having the features described in the preceding paragraph.

[0029] The invention also encompasses such a syringe, together with a
source of foam either in assembled form or in kit form.

[0030] With this syringe, the method of dispensing foam comprises:
[0031] (a) connecting the foam source to the plunger foam inlet (unless
the source is supplied already so connected); [0032] (b) generating a
substantially continuous flow of foam from the said source and allowing
an initial quantity of foam to flow from the plunger inlet into the waste
container such as to fill or substantially fill the waste container; and
[0033] (c) causing foam to flow from the plunger inlet to the plunger
outlet and thence through the syringe nozzle for use.

[0034] Preferably, step (c) includes the step of causing sufficient back
pressure to build up in the waste container to open the pressure
sensitive valve thereby allowing flow of foam through the waste container
outlet.

[0035] According to a second aspect of the invention, a syringe for
dispensing foam comprises: [0036] (a) a syringe plunger having an
internal waste chamber with an inlet; and [0037] (b) a syringe barrel
having a nozzle and a bore to receive the plunger; wherein the plunger
inlet is in communication with the syringe nozzle.

[0038] Preferably the internal waste chamber is provided with a vent which
may either be a hydrophobic vent or a hole or some other means for
allowing air to escape whilst substantially preventing foam from escaping
from the chamber. The chamber may have one or more flexible walls and may
be substantially empty/airless in its initial state prior to filling with
foam. In the latter case, the flexible chamber may be contained within a
space defined by rigid walls of the plunger, in which case it may be
preferable to have vents in the said rigid walls to allow air between the
chamber walls and the said rigid plunger walls to escape when the chamber
is filling with foam.

[0039] In an alternative arrangement, the waste chamber may simply
comprise a bag located behind the face of the plunger, but with an inlet
through the front face of the plunger whereby the bag communicates with
the main chamber of the syringe. The bag is preferably inextensible.

[0040] The inlet to the chamber is preferably adjacent the syringe nozzle
when the plunger is in its fully depressed state. The chamber may be
substantially cylindrical with substantially rigid walls, in which case
it may be defined by an end wall adjacent the syringe nozzle when the
plunger is depressed, in which end wall the said inlet is located.
Alternatively, the chamber may have no end wall, in which case the
chamber comprises a back wall remote from the syringe nozzle and a
cylindrical wall.

[0041] The second aspect of the invention also encompasses a syringe as
defined above together with a source of foam, e.g. a pressurized canister
adapted for generating foam, either in assembled form or in kit form.

[0042] A method of dispensing foam according to the second aspect and
using a syringe as defined above may comprise the steps of: [0043] (a)
connecting a syringe as defined above to a source of foam or
alternatively providing an assembly comprising a source of foam having an
outlet connected to the syringe nozzle; and [0044] (b) dispensing a
continuous flow of foam into the syringe from the source; [0045] (c)
whereby the flow of foam initially enters the waste chamber such that
foam fills or substantially fills the said waste chamber; and [0046] (d)
the flow of foam subsequently pushes the syringe plunger back in the
syringe barrel and starts to fill the syringe.

[0047] According to a third aspect of the invention a syringe for
dispensing foam comprises: [0048] (a) a syringe barrel comprising a
cylindrical side wall and a front end wall in which is located a syringe
nozzle; and [0049] (b) a syringe plunger having an end face which seals
against an interior surface of the cylindrical side wall of the syringe;
[0050] (c) wherein the side wall of the barrel is provided with an outlet
at a position remote from the nozzle.

[0051] Preferably the end face of the syringe plunger, or a portion of it,
makes an oblique angle with the longitudinal axis of the syringe barrel.

[0052] A waste container may be fitted to the outlet or connected to it
via tubing. The waste container may have substantially rigid walls or may
have one or more flexible walls. A hydrophobic vent or a vent hole may be
provided in a wall of the waste container.

[0053] The third aspect encompasses an assembly or a kit comprising two or
more of: a syringe as described above, a waste container as described
above and a foam source (e.g. a pressurized canister adapted for
generating foam).

[0054] The third aspect of the invention encompasses a method of using the
apparatus described above comprising the steps of:-- [0055] (a)
connecting a syringe as defined above to a source of foam or
alternatively providing an assembly comprising a source of foam having an
outlet connected to the syringe nozzle, with the syringe plunger drawn
back such that the syringe nozzle and syringe outlet communicate; and
[0056] (b) dispensing a continuous flow of foam into the syringe from the
source; [0057] (c) whereby foam flows into the syringe and fills or
substantially fills it, with an initial portion of the foam being
directed out of the syringe outlet to waste.

[0058] Preferably, a waste container is fitted to the syringe outlet or
connected to it by tubing, or such an arrangement is provided ready
assembled. Also, preferably the syringe is held in a vertical orientation
to help the exit of bubbles to waste. This helps large bubbles to rise
and be ejected before too much foam is wasted.

[0059] Once it is determined that the foam passing out of the outlet is of
substantially consistent, acceptable quality, the flow of foam from the
generator is stopped and the plunger depressed to seal off the outlet
from communication with the syringe nozzle. The waste chamber and the
source may then be disconnected and the syringe full of foam is ready for
use.

[0060] If the end face of the plunger is formed obliquely, this helps
prevent dead spots in the flow of foam from the source to the outlet,
thus helping to ensure that all or substantially all the poor quality
foam is removed from the syringe without too much wasting of good foam.
If there is any poor quality foam retained in the syringe, it is likely
to be in the vicinity of the plunger face, e.g. if the foam is stiff or
if the syringe is held vertical or at least with the nozzle pointing
downwards at an angle throughout the procedure. Having the plunger face
at an oblique angle to the end wall of the syringe barrel means that the
syringe is never completely emptied of foam, and any poor foam will be
retained in the space formed between the end wall of the barrel and the
oblique face of the plunger.

[0061] The sequence of operation may thus be: [0062] 1. Continuously
dispense foam into the syringe with the plunger drawn back past the side
outlet until all or substantially all foam of poor quality (either from
the start up phase of the foam source or due to air pockets in the
syringe or in any system interposed between the syringe and the source)
has been driven out of the outlet. [0063] 2. Before disconnecting the
syringe from the source of foam, cease generating or dispensing foam into
the syringe. [0064] 3. Push the plunger past the side outlet. [0065] 4.
Disconnect the foam source.

[0066] Further features and details of the invention will be apparent from
the following description and from the accompanying drawings in which:--

[0067] FIG. 1 is a schematic sectional view of a first embodiment of
syringe and system;

[0068]FIG. 2 is a schematic sectional view of a second embodiment of
syringe and system;

[0069]FIG. 3 is a schematic sectional view of a third embodiment of
syringe and system;

[0070] FIG. 4 is a schematic sectional view of a fourth embodiment of
syringe and system;

[0071]FIG. 5 is a schematic sectional view of a fifth embodiment of
syringe and system;

[0072]FIG. 5a is a schematic sectional view of a modified version of the
fifth embodiment;

[0073] FIG. 6 is a sectional view of a sixth embodiment of syringe and
system; and

[0074]FIG. 7 is a sectional view of a pressurized canister for generating
foam, which canister forms part of the first to sixth embodiments.

[0075] Referring firstly to FIG. 1, a system is shown for filling a
syringe with a clinical grade foam made with a sclerosant liquid, e.g. 1%
polidocanol solution, for injection into varicose veins. The canister 40
shown schematically in FIG. 1 is shown in more detail in the sectional
view of FIG. 7. A dip tube 44 communicates with an internal valve 42
which functions in a conventional way to open the canister when it is
depressed. Mounted on top of the valve is a stack of mesh elements 43
communicating with a canister nozzle 41, the whole mesh stack arrangement
being slidably mounted such that the canister nozzle 41 may be depressed
to open the valve 42.

[0076] The canister 40 contains sclerosant liquid as described above,
together with a gas mixture comprising carbon dioxide and oxygen at 3 bar
gauge pressure.

[0077] The syringe 1 comprises a barrel 10 which has a front end wall 13
in which is located a conventional luer nozzle 11, a cylindrical side
wall 14 and an opening 15 at the back end. Finger grips 12 are located at
the back end as is conventional. Received within an internal bore 16 of
the barrel 10 is a plunger 20 with a seal formation 21 at the front end
thereof which seals with the bore 16 of the barrel as is conventional.

[0078] The plunger 20 of formed of a plastics moulding having a front end
wall 22 and a cylindrical wall 23. The back end of the plunger moulding
has no wall but has a resilient plug 24 fitted therein. Located in the
resilient plug 24 is an inlet 25 which includes a one way valve 26 of
conventional design. Extending within the plunger 20 is a tube 27 which
communicates between the inlet 25 and an outlet 28 in the front end wall
22 of the plunger 20. The outlet 28 is located such that it is in
registry with the bore of the luer nozzle 11 when the plunger is fully
received into the barrel 10.

[0079] The inlet 25 is designed to make a seal with the nozzle 41 of a
pressurized canister 40 for generating foam. As described above, foam is
dispensed when the canister nozzle 41 is depressed, thereby opening the
internal valve 42 in the canister 40, and propelling gas and liquid
through a stack of mesh elements 43 and out of the nozzle 41 as foam.

[0080] Fitted onto the front end of syringe is a waste container 50. The
waste container comprises a flexible bag 51 of e.g. of inextensible film
or foil. The container 50 is equipped with a rigid tube 52 communicating
with the interior of the bag 51, with the walls of the bag sealed around
the tube 52. The outer end of the tube 52 is formed as a female luer
connector 53.

[0081] In operation, the syringe, with the plunger 20 in the fully
depressed position as shown in FIG. 1, is fitted to the canister by
inserting the canister nozzle 41 into the complementarily-formed plunger
inlet 25. A waste container 51 is then fitted to the syringe nozzle 11 so
as to seal around the nozzle.

[0082] The syringe 1 is then pushed towards the canister 40 by applying
force to the syringe finger grips 12, whereby the canister nozzle 41 is
pushed in so as to activate the canister valve and generate a flow of
foam from the canister. Foam flows from the canister 40 into the inlet
25, past the valve 26, through the tube 27, out of the plunger outlet 28
and then out of the syringe nozzle 11 and into the waste container 50.

[0083] Pressure on the syringe towards the canister is maintained so that
the flow from the canister 40 is continuous. The initial portion of this
flow consists of foam of inconsistent and poor quality; this foam is fed
into the container 50 as described above, together with air from the tube
27 in the plunger and from the luer nozzle 11, and from any other dead
spaces in the system. This air may become incorporated in the foam in
which case the quality of the foam may be affected; whether or not this
happens, the air is dispensed from the syringe nozzle 11 into the waste
container 50.

[0084] The flexible walls of the waste container, which is initially
substantially airless, allow it to expand as foam enters, until it can
hold no more foam. As foam continues to flow from the canister 40, a back
pressure is built up which soon becomes sufficient to overcome the
friction between the plunger seal 21 and the inner surface 16 of the
syringe barrel 10. The plunger 20 then moves back and the syringe barrel
fills with substantially homogeneous, good quality foam.

[0085] The walls of the syringe barrel 10 are transparent, which allows
the quality of the foam to be checked by the user. The user may be
looking for homogeneity, bubble size, density or stiffness, all of which
may be discerned to some degree by the naked eye: when the bubbles are
microscopic, the foam may take on a smooth, white appearance. The volume
of the waste container is about 10% of that of the syringe and this has
been determined to ensure that both the initial quantity of poor foam
together with any trapped air in the system can be dispensed into the
container before the waste container becomes full. The visual check on
the contents of the syringe could therefore be dispensed with, but is
nevertheless desirable to ensure nothing has gone wrong.

[0086] Once a sufficient quantity of foam has been dispensed into the
syringe, pressure on the canister nozzle is released, thereby shutting
off the flow of foam. The waste container 50 may then be removed and the
foam-filled syringe is ready for use. Use of the syringe 1 involves
dispensing foam down a line to a cannula inserted into the venous system
of a human patient. When the plunger 20 is depressed to dispense foam, it
will be appreciated that the one way valve 26 on the plunger inlet 25
prevents flow of foam back out of the inlet.

[0087] A modification to this system is to provide a valve 54 in the tube
52 of the waste container 50. At the start of the filling process, this
valve 54 is open; when foam is being delivered, the user may determine
from visual inspection that the foam in the syringe is of acceptable
quality even though the bag 51 is not yet full. In this case, the user
may shut off the valve 54 so that the plunger starts to move back and the
syringe to fill.

[0088] In another modification, the waste container 50 could comprise a
rigid vessel, in which case a vent would be provided to allow displaced
are to be exhausted as foam entered the container.

[0089] A second embodiment is shown in FIG. 2. Reference numerals for
parts corresponding to parts of the first embodiment correspond, with the
series starting at 101. In the second embodiment, the waste container 150
is incorporated within the plunger 120.

[0090] The syringe barrel 110 and its various parts are the same as for
the first embodiment. The plunger 120 is almost the same as that of the
first embodiment as regards its external features, except that it has a
small vent hole 130 in its cylindrical side wall--the operation of this
feature will be described below. The inlet 125, fitted with a one-way
valve 126, communicates with a waste container 150 located within a
cavity in the plunger defined by the plunger walls 122, 123 and plug 124.
The canister 140, shown schematically in FIG. 2, is the same as that of
the first embodiment and the same as that shown in FIG. 7. The waste
container 150 comprises an elongate bag 151 extending the length of the
plunger. The inlet 125 is aligned so as to direct foam along the length
of the bag 151 and thus fill the bag from the end 155 furthest from the
inlet.

[0091] Adjacent the inlet 125 is a burst seal 156 in the wall of the bag
151. The burst seal 156 communicates with a tube 127, also located within
the plunger, and which communicates in turn with an outlet 128 analogous
to the outlet 28 in the first embodiment. In FIG. 2, the outlet 128 is
shown as being slightly to one side of the syringe nozzle 111;
alternatively, and preferably, the nozzle 111 and outlet 128 are in
registry with each other.

[0092] The volume of the bag 151 is about 5-10% of the volume of the
syringe barrel when the plunger is fully back. In use, similar to the
first embodiment, the syringe is pressed against the canister with the
canister nozzle 141 fitted to the inlet 125, whilst the plunger 120 is in
its fully depressed state as shown. Foam is then dispensed from the
canister 140, through the nozzle 125 and into the bag 151. The jet of
foam issuing from the canister nozzle 125 passes down to the end 155 of
the bag 151 and the bag fills from this end. As the bag fills from its
initially airless state, it displaces air around it in the cavity defined
in the plunger; this is released through the vent 130 in the side wall of
the plunger. In a modification, the tube 157 extends from the nozzle 125
and terminates at the blind end of the bag 151. This allows "bad" foam to
accumulate distal to the pressure break valve 156, so that when the break
valve 156 is broken, only good quality foam flows through the tube 127 to
the outlet 128.

[0093] Once the bag 151 is full of foam, the quality of foam being
dispensed from the canister is consistently good. The volume of the bag
is such that the inlet end of the bag will contain good foam. Any dead
spaces in the inlet 125 and the canister nozzle 141 are now filled with
good quality foam. However, the tube 127 still contains air.

[0094] At this point continued generation of foam by the canister causes a
back pressure to build up in the waste bag 151, sufficient to burst the
seal 156 on the bag. The flow of foam is then diverted through the
opening created by bursting the seal 156 and then into the tube 127. Foam
at the inlet end of the bag may be displaced and may pass into the tube
127, but as discussed above this foam will be of good quality.

[0095] Foam passing into the tube 127 drives out air from the tube and
then passes out through the outlet 128 and syringe nozzle 111. When the
user observes foam exiting the syringe nozzle 111, he or she puts a
syringe nozzle cap 102 on the luer nozzle 111 to block the flow. The
plunger then moves back and the syringe fills.

As with the first embodiment, when the syringe is full, generation of
foam is stopped and the canister removed. Before delivering foam from the
syringe into a patient, the nozzle cap 102 is removed. As with the first
embodiment, the valve 126 prevents foam flowing back out of the inlet 125
when the plunger is depressed to deliver foam through the nozzle 111.

[0096] The second embodiment is not the preferred one, since the user
still needs to expel a small quantity of waste foam from the nozzle of
the syringe and, preferably, to monitor this foam to ensure its quality.
However, the majority of the waste foam is contained and the arrangement
is neater than that of the first embodiment since the bag is contained
within the plunger.

A third embodiment is shown in FIG. 3. Again, similar parts are
designated by numbers corresponding to those used in the descriptions of
the first and second embodiments, the series starting at 200. The
canister 240 is identical to that of the first and second embodiments, as
shown in more detail in FIG. 7. This embodiment is similar in most
respects to the second, the waste container being rigid rather than
flexible. The waste container 250 is an annular shape extending for most
of the length of the plunger as shown in the Figure, apart from a flat
cylindrical portion 257 at the inlet end. The container 250 is defined by
the end and side walls 222, 223 and the bung 224 of the plunger, together
with a central rigid tubular portion 227 of the plunger. In the front end
wall 222 of the plunger 220 are located hydrophobic vents 229. These are
composed of a fine mesh or porous material such as a porous PTFE film.
Their purpose is to allow air to pass through but not liquid (or foam).
Located in the region of the inlet end of the plunger 220 is a burst seal
256 which seals the interior of the container 250 from the interior of
the tubular portion 227. In use, the third embodiment works in an
analogous manner to the second embodiment. Foam is generated by the
canister when the syringe is pressed against it to depress the canister
nozzle 241 in order to actuate the canister valve (see FIG. 7). Foam
flows from the canister into the inlet 225 and is carried by its own
momentum to the front end of the waste container 250, air being displaced
through the hydrophobic vents 229. Foam builds up in the container until
it is full, the container being sized such that the foam in the region of
the inlet 225 is of good quality. A back pressure accumulates and bursts
the seal 256, allowing foam to pass down the central tube 227. The
remainder of the operation of the third embodiment is exactly as
described for the second embodiment. This embodiment is not preferred,
for similar reasons to those explained above in connection with the
second embodiment. In addition to those issues, in the third embodiment
the hydrophobic vents may become blocked with foam and prevent air
escaping from the waste container 250. A fourth embodiment is shown in
FIG. 4. As before, reference numerals designating similar parts
correspond, but with the sequence starting at 301. In this embodiment,
unlike the first to third described above, the syringe is filled from the
front, through the main syringe nozzle 311. The barrel 310 of the syringe
301 is identical to that of previous embodiments, and is conventional.
The canister 340 is identical to that of the first to third embodiments,
as shown in FIG. 7. A tubular connector 345 is provided to make a sealing
connection between the canister nozzle 341 and the syringe luer nozzle
311. One end 346 of the connector is adapted to receive the canister
nozzle 341 whilst the other is formed as a female luer connector 347 to
fit the luer nozzle 311 of the syringe. The plunger 320 is formed
conventionally with a rear flange 331 to assist manual actuation, whilst
the shaft 332 of the plunger is formed, also conventionally, with a
cruciform section. At the front end of the plunger 320, a waste container
350 is located. The container 350 is defined by a relatively short
cylindrical side wall 323, a front end wall 322 and a rear end wall 333.
An inlet aperture 334 is provided in the front end wall 322 which is in
registry with the syringe nozzle 311 when the plunger 320 is in its fully
depressed position. Hydrophobic vents 329 are provided in the rear end
wall 333 of the container 350. The external cylindrical surface of the
container forms a seal with the internal surface 316 of the barrel 310.
The front end face 322 of the container is equivalent to the front face
of the plunger in the other embodiments. In use, the syringe nozzle 311
is connected to the canister nozzle 341 by means of the connector 345 as
shown in FIG. 4. The syringe is pressed against the canister 340, thereby
causing foam to be generated by the canister as previously described in
connection with the other embodiments. The foam flows into the syringe
nozzle 311 and then into the waste container 350. Air in the waste
container is displaced out though the hydrophobic vents 329 whilst foam
is retained in the container. The volume of the waste container is about
10% of that of the syringe. Once full, as with previous embodiments, it
is reasonably certain that the foam will be of consistent, acceptable
quality. At this point pressure will build in the syringe as foam
continues to be generated by the canister. The plunger 320 will be pushed
back and the syringe filled. It is possible that a little of the foam in
the waste container 350 will leak out of the inlet aperture 334 into the
main chamber of the syringe. However, the foam adjacent the inlet of the
container 350 will be good quality foam and therefore this is not too
important. Once the syringe is full, all that is required is to stop the
generation of foam and detach the syringe, which is ready for use.
Referring now to FIG. 5, a fifth embodiment is shown which is similar in
most respects to the fourth. As before, reference numerals designating
similar parts correspond, but with the sequence starting at 401. In this
embodiment, a flexible waste bag 451 is provided within a chamber 458 of
the syringe plunger 420. The barrel 410, connector 445 and canister 440
are identical to the fourth embodiment described above. The plunger 420
is also identical to that of the fourth embodiment except for the front
end of the plunger 420 which houses a waste container bag 451. The front
of the plunger 420 is formed, similar the fourth embodiment, as a short
hollow cylinder having a cylindrical side wall 423, front end wall 422
and rear end wall 433. In the front end wall is provided an inlet 434
which communicates a waste bag 451 located in a chamber 458 defined by
the walls 422, 423, 433. The waste bag 451 is in a substantially
collapsed state so that it contains little or no air. Provided in the
rear end wall 433 of the chamber 458 are vent holes 429. In use, the
fifth embodiment operates almost identically to the fourth. Instead of
entering a rigid waste container, foam from the canister enters a
flexible waste bag 451 which, as it fills, displaces air from the chamber
458 through vents 429. When the waste bag is full, the syringe plunger is
pushed back and the syringe fills with consistent, good quality foam. As
with the fourth embodiment, once the syringe is full the canister is shut
off and the syringe simply detached for use. A modification of the fifth
embodiment is shown in FIG. 5a, which illustrates only the syringe (the
other elements being the same as for FIG. 5). The syringe comprises a
conventional syringe barrel 410. The plunger 480 has a rear flange 481 to
assist application of pressure by hand. The shaft of the plunger
comprises four parallel shaft members 482. The front end of the member
comprises an end wall member 483 with a sealing region 484 around its
periphery for sealing against the internal surface 416 of the barrel. In
the centre of the end wall is an inlet 485 which, when the plunger is
depressed fully, is in registry with the luer nozzle 411 of the syringe.
Extending from the rear face of the plunger 480 is a boss 486 through
which extends the inlet 485. The boss 486 terminates in a flange 487
around which an airless waste bag 451 is retained. The operation of this
modification is exactly the same as that of the fifth embodiment. A sixth
embodiment is shown in FIG. 6. The system shown comprises a canister of
identical design to the first to fifth embodiments and shown in detail in
FIG. 7. Also provided is a connector 545 of identical design to the
connector described above in connection with the fourth and fifth
embodiments. As before, reference numerals designating similar parts
correspond, but with the sequence starting at 501. In this embodiment, an
additional luer nozzle 515 is provided in the side wall 514 of the
syringe barrel 510, towards the rear of the syringe, for dispensing waste
foam. In all other respects the syringe barrel 510 is conventional and
the same as in the other embodiments. The plunger 520 has a conventional
rear flange 531 and shaft 532 of cruciform section, as in the fourth and
fifth embodiments. The end wall 522 of the plunger makes a seal 521 with
the interior surface 516 of the barrel 510 as is conventional, but the
wall is inclined at an oblique angle to the longitudinal axis of the
syringe 501. In use, the syringe is pressed against the canister as
previously described and foam is dispensed into the syringe with the
plunger in the fully depressed position (not the position shown in the
Figure). Although not shown in the Figure, it will be appreciated that
when the plunger is fully depressed, there will still be a space defined
between the face of the plunger and the interior of the end wall of the
syringe barrel. The initial poor quality foam will enter this space, but
will not fill it since air will be trapped in the space. Once a back
pressure has built up, the plunger 520 will move back and the syringe
fill with foam. When the plunger reaches the position shown in FIG. 6, it
will stop moving back since the foam will have a low resistance path into
the waste bag 551 which is substantially airless in its initial state.
The poor quality foam initially dispensed into the syringe will be the
first to pass into the waste bag, assisted by the inclined face of the
plunger. After a quantity of foam has been dispensed into the waste bag
551, the syringe is filled exclusively with consistent, good quality
foam. The user may determine that this state has been reached by
observing the foam through the transparent walls of the syringe barrel
510. Alternatively or in addition the user may wait until the waste bag
is full at which point a back pressure will build up which the user may
feel on the syringe plunger as it starts to move. However this state is
determined, the user then shuts off the canister, moves the syringe
plunger the few millimetres necessary to close the second luer 515, then
removes the canister and waste bag. The syringe full of foam is then
ready for use. In a modification of this embodiment, the waste container
described above, with a predetermined volume, is omitted. The principle
of waste foam exiting a nozzle on the side of the syringe barrel applies
whether a container is attached or not; it is therefore possible to omit
it or to provide some other form of container which is not designed to
fill and provide a back pressure indicating that sufficient foam has been
wasted. In this modification, the user simply determines by observation
when all the foam in the syringe barrel is of adequate quality, or
alternatively wastes foam for a predetermined time, and then stops
generation of foam and proceeds as before.